The fourth child and second son among ten children, Marmaduke was born on his father's plantation near Arrow Rocke in Saline County, Missouri. His mother was Lavinia Sappington Marmaduke. His father, Meredith Miles Marmaduke (1791–1864), was the eighth Governor of Missouri. His great-grandfather, John Breathitt, had served as the Governor of Kentucky from 1832–1834, dying in office.
Marmaduke attended Chapel Hill Academy and the Masonic College in Missouri, before attending Yale University for two years and then Harvard University for another year, leaving to accept an place at West Point.
He was 28 years old when the Civil War began.
Congressman John Phelps appointed Marmaduke to the United States Military Academy, where he graduated in 1857, placed 30th out of 38 students. He briefly served in the First United States Mounted Rifleman, before being transferred to the Second United States Cavalry under Albert Sidney Johnston.
Marmaduke was on duty in the New Mexico Territory in the spring of 1861 when he received news that Missouri had seceded from the Union. He traveled home and met with his father, an avid Unionist. Even though the news was false, Marmaduke finally decided to resign from the United States Army, effective April 1861.
|Battle of Booneville|
|Albert Sidney Johnston|
General Sterling Price ordered both officers to remain in their quarters in an attempt to prevent the duel. However by an unfortunate series of mishaps, the orders were not delivered to Walker. At dawn on Sunday, September 6, Walker and Marmaduke squared off with Colt Navy revolvers on the north bank of the Arkansas River near Little Rock. Both fired and missed. Marmaduke then recocked and fired a second time, mortally wounding Walker in the right side, just above the beltline. Walker forgave Marmaduke when the latter offered his assistance.
|Lucius "Marsh" Walker|
Marmaduke was briefly placed under arrest for his participation in the duel.
Marmaduke later commanded a cavalry division in the Trans-Mississippi Department, serving in the Red River Campaign. During this period, Marmaduke once again was involved in controversy. Commanding a mixed force of Confederate troops, including Native-American soldiers of the 1st and 2nd Choctaw Regiments, Marmaduke defeated a Federal foraging detachment at the Battle of Poison Springs, Arkansas on April 18, 1864. Marmaduke's men were accused of murdering African-American soldiers of the First Kansas Colored Volunteer Infantry (later designated the 79th U.S. Colored Infantry). Marmaduke and other white officers claimed that the accusations of illegal killings were overblown, and blamed any murders that may have happened on the Choctaw troops who, in the words of one while Confederate, did "kill and scalp some" of the black troops. Marmaduke was hailed in the Confederate press for what was publicized as a significant southern victory.
Marmaduke commanded a division in September–October 1864 into Missouri, where Marmaduke was captured at the Battle of Mine Creek. While still a prisoner of war at Johnson's Island in Ohio, Marmaduke was promoted to major general in March 1865. He was released after the war ended.
|Johnson's Island Prison Camp|
After the war, Marmaduke went on a tour of Europe before returning to St. Louis. He worked briefly for an insurance company, whose ethics he found contrary to his own. He then edited an agricultural journal, and publicly accused the railroads of discriminatory pricing against local farmers. The governor soon appointed Marmaduke to the state's first Rail Commission. Marmaduke decided to enter politics, but lost the 1880 Democratic nomination for governor to former Union general Thomas Crittenden, who had strong support and financial backing from the railroads. Undeterred, Marmaduke campaigned four years later for Governor of Missouri at a time when public opinion had changed, and railroad reform and regulation became more in vogue.
Like his great-grandfather, Marmaduke died while in office, passing away from pneumonia on December 28, 1887, in Jefferson City on the same day that he was supposed to host his yearly Christmas party in the mansion for the town's children.
He was buried in the City Cemetery. His tombstone reads: "He was fearless and incorruptible."